The present invention relates to a toner density control device, being adapted to an image forming apparatus such as a copier, a printer, a facsimile or the like wherein development is performed in such a manner that an electrostatic latent image is formed, and toner is applied thereto.
An explanation will now be made taking a copier having a movable original platen for an example of the image forming apparatus.
A copier of this type is provided with a toner sensor for detecting the density of toner stored in the developing section.
Generally, in the process of image formation, mechanical vibration occurs to the whole body of a copier when the original platen changes its movement from the return direction to the exposing direction and, conversely, from the exposing direction to the return direction after the completion of exposure. This vibration disturbs the flow of toner in the developing section, causing erroneous detection of toner density by the toner sensor and irregularity in the waveform of the output signal therefrom (this irregularity is generally called as a whisker).
FIG. 7 shows an example of the influence of the above-described vibration upon the output of the toner sensor. FIG. 7 is a graph showing a part of the output waveform of the toner sensor in the case a plurality of copying operations for a single document are continuously carried out, where coordinates are time on the abscissa and output voltage on the ordinate. The irregularity of the waveform indicated by part i of this graph is caused by the vibration generated when the original platen commences its return movement for starting copying operation, and the irregularity of the waveform indicated by part ii is caused by the vibration generated when the original platen stops its return movement, and the irregularity of the waveform indicated by part iii is caused by the vibration generated at a moment when the original platen begins to move for exposure.
As described above, mechanical vibration in a copier often affects the output of a toner sensor, that is, mechanical vibration brings about erroneous detection of toner density, resulting in an inappropriate toner supply in compliance with the output of the toner sensor based on the above erroneous detection. This considerably deteriorates the accuracy of the toner density control.
Such a drawback occurs not only in the aforesaid copier having a movable original platen but also in a copier having a movable exposure lamp and movable mirror, a facsimile and the like.